diff --git a/src/Server/Handler/Request/CallToolHandler.php b/src/Server/Handler/Request/CallToolHandler.php
index 254e8388..0b632d41 100644
--- a/src/Server/Handler/Request/CallToolHandler.php
+++ b/src/Server/Handler/Request/CallToolHandler.php
@@ -68,7 +68,7 @@ public function handle(Request $request, SessionInterface $session): Response|Er
         } catch (ToolNotFoundException $e) {
             $this->logger->error('Tool not found', ['name' => $toolName, 'exception' => $e]);
 
-            return new Error($request->getId(), Error::METHOD_NOT_FOUND, $e->getMessage());
+            return Error::forInvalidParams($e->getMessage(), $request->getId());
         }
 
         $inputSchema = $reference->tool->inputSchema;
diff --git a/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php b/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
index 87a696be..47351dc0 100644
--- a/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
+++ b/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
@@ -183,7 +183,7 @@ public function testHandleToolNotFoundExceptionReturnsError(): void
 
         $this->assertInstanceOf(Error::class, $response);
         $this->assertEquals($request->getId(), $response->id);
-        $this->assertEquals(Error::METHOD_NOT_FOUND, $response->code);
+        $this->assertEquals(Error::INVALID_PARAMS, $response->code);
     }
 
     public function testHandleToolCallExceptionReturnsResponseWithErrorResult(): void